NCERT Solutions for Class 8 Science Chapter 17 – Stars and the Solar System

 Inner planets are the first four planets closest to the Sun-Mercury, Venus, Earth, and Mars.

Therefore, (i) Inner planets – e) Earth, g) Mars

Outer planets are the last four planets closest to the Sun – Jupiter, Saturn, Uranus, and Neptune

Therefore, (ii) Outer planets – a) Saturn

A constellation is a group of stars forming a definite shape.

Therefore, (iii) Constellation – c) Great Bear, f) Orion

A satellite of the earth is the moon. 

Therefore, (iv) Satellite of earth – d) Moon

 

 The part of the sky where we can find Venus if it is visible as an evening star is the west side of the sky.

 

The largest planet of the solar system is Jupiter and the smallest planet is Mercury.

 

A constellation is a group of stars forming a definite shape. The two constellations are: 

i) Orion: It is located on the celestial equator and is visible throughout the world. It is a constellation in the night sky.

ii) Great Bear: It is located in the northern sky.

 

(c) A constellation

A constellation is not a member of the solar system because it is a group of stars forming a definite shape whereas an asteroid, satellite, and comet are a part of the solar system.

 

a) Ursa major is located in the northern sky. 

The sketch of the Ursa Major is:

b)  Orion is located on the celestial equator and is visible throughout the world. It is a constellation in the night sky.

The sketch of the Orion is:

(Image Will Be Updated Soon)

 

The two other objects other than planets that are members of the solar system are:

i) Stars: Stars are celestial bodies made up of gases; they are huge in size and have very high temperatures

ii) Asteroid: Asteroids are small, rocky objects that orbit the sun.

 

 We locate the Pole Star with the help of Ursa Major with the help of the three stars at the end of Ursa Major. To do so, create a straight line passing through the last three stars and extend that line in the north direction. The star seen in that direction is the Pole star.

 

No, the stars in the sky do not move because the Pole star is located above the axis of rotation of the Earth in the north direction. And hence it appears to be stationary and all other stars in the sky appear to move from East to West.

 

a) Sirius

Sirius is not a planet of the sun but a star. The planets of the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

 

 (a) we can see only that part of the moon that reflects light towards us.

Phases of the moon occur because the source of light of the moon is the Sun, it does not have its light and hence, it reflects the light coming from the sun and we can only see that part of the moon that reflects light towards us.

 

 Stars are very far away from each other and the standard km notation of the distance seems unrealistic to use for denoting the distance between stars and hence, a much convenient and larger unit is used for expressing these distances which are known as light-years. It helps to make calculations and imagination easy.

One light-year denotes the distance traveled by light in one year.

1 Light Year = 9.46×

10

12

 km

1 Light Year = 9.46×1012 �� 

A star is eight light-years away from the Earth means that a star is

8× 9.46×

10

12

=7.568×

10

13

 km

8× 9.46×1012=7.568×1013 �� away from the Earth.

 

The shape of Earth and Jupiter is a sphere. Let the radius of Earth be

R

E

�� and the radius of Jupiter be

R

J

��.

Given,

R

J

=11⋅

R

e

��=11⋅��    …..(1)

We know that the volume of a sphere of the radius

r

� is

4

3

π

r

3

43��3. Therefore, 

The volume of Earth,

V

E

=

4

3

π

R

3

E

��=43���3   …… (2)  

The volume of Jupiter,

V

J

=

4

3

π

R

3

J

��=43���3   

But from (1),

R

J

=11⋅

R

e

��=11⋅��. Hence, Volume of Jupiter,

V

J

=

(11)

3

4

3

π

R

3

E

��=(11)343���3  ...(3)

From (2) and (3), the ratio of the volumes of Jupiter and the Earth is

 

V

J

V

E

=

(11)

3

4

3

π

R

3

E

4

3

π

R

3

E

����=(11)343���343���3

⇒

V

J

V

E

=

(11)

3

⇒����=(11)3

∴

V

J

V

E

=1331

∴����=1331

This means that Jupiter can accommodate

1331

1331 earth.

 

a) The planet which is farthest from the sun is Neptune.

b) The planet which appears reddish in color is Mars.

c) A group of stars that appear to form a pattern in the sky is known as a Constellation. 

d)  A celestial body that revolves around a planet is known as a satellite.

e) Shooting stars are actually not stars. 

f)  Asteroids are found between the orbits of Mars and Jupiter.

 

a) True

Stars are a member of the solar system.

b) True

Mercury is the smallest planet and all other planets are larger than mercury.

c) False

Neptune is the farthest planet in the solar system. 

d) True

INSAT is a man-made satellite.

e) False

There are eight planets in the solar system. The planets of the sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

f) False

During winters, the constellation Orion is visible with naked eyes.

 

The figure of the solar system is incorrect because 

a) The positions of Mars and Venus are interchanged.

b) The positions of Uranus and Neptune are interchanged.

c) The asteroid belt which is between Mars and Jupiter should be present between Jupiter and Saturn.

The correct figure is: